Mixing finely divided contact particles in a dense fluid bed



D. s. BOREY 3,091,594

MIXING FINELY DIVIDED CONTACT PARTICLES IN A DENSE FLUID BED May 28,1963 Filed July 1, 1959 FIG.-l

Daniel 3. Borey lN'VENT-OR ay PATENT ATTORNEY w in:

hit Site 3,091,594 MIXING FINELY DIVIDED CONTACT PARTICLES IN A DENSEFLUID BED Daniel S. Borey, Chatham, NJ., assignor to Esso Research andEngineering (Tompany, a corporation of Delaware Filed July 1, 1959, Ser.No. 824,426 6 Claims. ((11. 252-417) This invention relates to methodand apparatus for obtaining improved mixing in a dense fluidized bed offinely divided contact of catalyst particles where the contact orcatalyst particles are introduced into the lower portion of the densefluid bed and contact or catalyst particles are withdrawn into anoverflow well from the upper portion of the dense fluidized bed of solidparticles. More particularly the invention relates to preventing orminimizing afterburning in the regeneration of finely divided solidcontact or catalyst particles in hydrocarbon conversion operations.

In reaction zones of the type above described it is desirable to obtaingood lateral mixing of the solid particles and gases or vapors passingup through the dense fluidized bed. While the invention is usefulgenerally to promote lateral mixing in a dense fluidized bed, it will bespecifically described in connection with the regeneration of fouled orpartially spent catalyst particles containing burnable carbonaceousdeposits. In the catalytic conversion or cracking of hydrocarbons, cokeor carbonaceous material is deposited on the catalyst particles and thecatalyst particles are then passed to a regeneration zone where the cokeor carbonaceous material is burned off with air or otheroxygen-containing gas. From the regeneration zone the regeneratedcatalyst particles are returned to the catalytic cracking or conversionzone.

In certain types of cracking units described in US. 2,589,124, grantedMarch 11, 1952, the fouled or coked catalyst particles from the reactionare passed into the dense turbulent fluidized bed of solids in theregeneration zone at one side thereof and regenerated catalyst orcontact solids are withdrawn from the top of the dense fluidized bed atthe opposite side of the regeneration zone. In certain of these unitsthe problem of afterburning has arisen because of relatively poorlateral mixing of the spent and regenerated catalyst in the densefluidized bed in the regeneration zone. The gases leaving the densefluidized bed in the regeneration zone contain carbon monoxide and someunburned hydrocarbons and in certain regions there is an excess ofoxygen. The combustion of coke or carbonaceous material in the densefluidized bed does not result in excessively high temperatures becausethere are suflicient solids to absorb the heat. However, wheninsuflicient solids are present in the gases leaving the dense bed,combustion of combustible material in the combustion gases may result inundesirable high temperatures which are harmful to the catalyst andcyclone separators and other equipment.

Afterburning does not occur to any great extent if the temperature ofthe gases leaving the regeneration zone is maintained below about 1075F. or if the oxygen content of the combustion gases is low, below about1.5% by volume of the combustion gases, but if afterburning starts, theburning continues and is self-sustaining due to the higher reaction rateat the higher temperature and the temperature goes up rapidly.

It has been found that flue or combustion gases leaving the densefluidized bed in the regeneration zone above the region of introductionof fouled catalyst to the regeneration bed contain relatively littleexcess oxygen. However, high oxygen concentrations exist in the flue orcombustion gases flowing up from the region above and near the overflowwell which promotes afterburning in the cyclone separators in thisregion. This is believed to be due to the relatively poor lateral mixingof the spent or coke containing catalyst particles in the densefluidized'be'd in the regeneration zone. The catalyst particles areregenerated in the region of the addition of the spent catalystparticles and flow generally upwardly and then across toward theoverflow well, but as the catalyst particles moving in this generalmanner are substantially regenerated by the time they reach the overflowwell, the oxygen-containing gas or air passing up through the densefluidized bed in the regeneration zone from the region around theoverflow well is not fully utilized and there is an oxygen breakthroughat this region.

According to this invention one or more sloped or inclined mixing tubesare submerged in the dense fluidized bed of solid contact or catalystparticles in the regeneration zone. The inlet to the mixing tube islocated near the top of the dense fluidized bed of solids in theregeneration zone and near the overflow well. The mixing tube slopes orextends down at an angle from the inlet to the bottom portion of thedense fluidized bed in the regeneration zone in the region near theplace where spent or coke-containing solids are introduced. The mixingtube is hollow without any obstructions and is submerged in the densefluidized bed of solids in the regeneration zone. I

No aeration gas is supplied to the solids in the mixing tube and assolids are supplied from the dense fluidized bed to the inlet end or topof the mixing tube, fluidizing gas disengages from the solids and thesolids flow down the mixing tube at an increased density, as for examplestandpipe density, and there is thus supplied a driving force forcirculating the solids from near the overflow well down to the region ofintroduction of the spent or coke containing solids in the regenerationzone and improved mixing of the solids in the dense fluidized bed isobtained. With this improved mixing there is a more uniform oxygencontent in the flue gases over the entire area of the dense fluidizedbed and the problem of afterburning is minimized. In a broaderapplication a slanting mixing tube is utilized to obtain better lateralmixing in a fluidized bed of solids where solids are introduced into thebed at one zone and withdrawn from the bed at another zone.

In the drawings:

FIG. 1 represents a vertical longitudinal cross section of one form ofapparatus adapted to carry out the present invention; and

7 FIG. 2 represents a horizontal transverse cross sectional view takensubstantially on line 2-2 of FIG. 1 with certain parts omitted tofacilitate the disclosure.

Referring now to the drawings, the reference character In designates acylindrical reaction vessel provided with a conical bottom portion 12and a gas inlet line 14. Arranged in the bottom of the reaction vesselin is a horizontal perforated distribution grid 16 for distributing thegas across the entire area of the reaction vessel. Supported on thedistribution grid 16 is a dense fluidizedturbulent bed of finely dividedsolids 18 having an upper level at 22 and a dilute phase 24 thereabove.The invention will be specifically described in connection with theregeneration of fouled catalyst from a catalytic cracking operation butit is to be understood that the apparatus can be used for otherreactions.

Arranged at the lower portion of the reaction vessel 10 is a solids orcatalyst inlet line 26 which extends through the distribution grid 16and for a short distance thereabove. Spent or fouled finely dividedcatalyst or contact particles are introduced into the bottom portion ofthe reaction vessel through solids inlet line 26. Arranged above the topof the inlet line 26 is a conical deflector 2'7. In catalystic crackingthe catalyst may be silica alumina, silica magnesia, activatedbentonitic clays and the like.

The catalyst is of a size between about 200 and 400 standard mesh andhas an average particle size between about 50 and 90 microns.

The gas introduced through bottom inlet 14 below the distribution grid16 is air when catalyst is to be regenerated in reaction vessel 16 andthe air is introduced at such a rate as to give a superficial velocityin the reaction vessel 1% above distribution grid 16 between about 1.5and 5.0 ft. per second and when using finely divided silica aluminacatalyst the density of the dense turbulent bed 18 will be between about20 and 30 lbs. per cubic foot.

Arranged on the opposite side within the reaction vessel it is anoverflow well or line 28 which extends through the distribution grid 16and up into the reaction vessel for about half the height of thereaction vessel or slightly less than /2 the height of the vessel 10.The overflow pipe 28 determines the level 22 of the dense fluidized bedin the vessel 16. The overflow well 28 is provided in its upper portionwith vertical slots 32 to give a smoother rate of catalyst withdrawaland to permit slight variations in the catalyst level 22 without largefluctuations in the rate at which catalyst overflows into the withdrawalwell 28. The withdrawal well 28 comprises a standpipe for building uppressure on the finely divided solids being circulated and the level ofthe catalyst in the withdrawal 28 is below the top of the well 28 asshown at 34. One or more fluidizing lines 36 may be provided forintroducing gas into the solids in the withdrawal well 28 to maintainthe particles in fluidized condition.

From the bottom of the withdrawal well 28 the regenerated catalyst orcontact particles are returned to a reaction zone (not shown) for use inthe catalytic conversion of hydrocarbons and spent or fouled catalyst iswithdrawn from such reaction zone and returned to the regenerator Itthrough solids inlet line 26. When operating as a regenerator thereaction vessel 10 will be maintained at a temperature about 1000 t-o1200 F., preferably 1100 to 1175 F.

The hot combustion or flue gases leave the bed 18 and pass up into thedilute or disperse phase 24 and as they contain entrained solid contactor catalyst particles they are passed through a solids separating meanssuch as a cyclone separator 42 arranged in the upper portion of thereaction vessel 10 in the region above the overflow well 28. Theseparator 42 has an inlet 44 and a dipleg 4-6 for returning separatedsolids to the dense fluidized bed 18. The gases leave the separator 42through line 48 to a second stage separating device suchas cycloneseparator 52 for removal of an additional amount of entrained solidsfrom the gases which are returned to the dense bed 18 through dipleg 54.The combustion or flue gases leave the cyclone separator 52 through line56. Both of the diplegs 4'6 and 54 extend below the level 22 of thedense fluidized bed 18.

In the arrangement shown with the solids inlet pipe 26 arranged in thelower portion of the reaction vessel and at one side and with theoverflow well extending to a higher level than the top of the inlet lineand arranged on the opposite side of the reaction vessel there isinsuflicient lateral mixing of the catalyst or contact particles duringregeneration and in some cases afterburning has resulted. The catalystparticles, after they are introduced by the solids inlet line 26, passgenerally upwardly above the inlet line 26 and after contact of the airwith the high coke content fouled catalyst in this region the combustiongases leaving the dense bed 18 from above the inlet line 26 haveessentially no oxygen content.

In order for the catalyst particles to get to the overflow well there islateral flow of the catalyst in the upper portion of the dense fluidizedbed and as the catalyst in the zone near this overflow well is nearlycompletely regenerated with a relatively low coke content, the oxygen inthe combustion air is not completely utilized. Thus, the air or otheroxygen-containing gas introduced through the perforated grid member 16adjacent to overflow well 28 passes upwardly through the dense fluidizedbed 18 with incomplete oxygen utilization and when this gas reaches theupper portion of the dense fluidized bed 18 it passes into the dilutephase 2 ifrom adjacent the top of the overflow well 28 containing excessoxygen and at a temperature of about ll25 and with an oxygenconcentration of about 3% by volume of the combustion gases. Under theseconditions afterburning (the oxidation of CO to CO may occur around theprimary cyclone separator 42 over the region of the overflow well 28because of the relatively low concentration of solids present in thedilute phase 24.

To minimize afterburning during regeneration and by better lateralmixing of the solids in the dense fluidized bed 18 eliminate thegradient of coke content on the catalyst across the diameter of thevessel and thereby achieve uniform oxygen content of the flue gasesleaving bed 18, a mixing tube 62 is provided which is submerged in thedense fluidized bed 18 and is inclined from the horizontal at an angleof between about 20 and 70, preferably about 45. The mixing tube 62 issuitably supported in the reaction vessel 10. The mixing tube 62 has anexpanded horizontally arranged top inlet 64 which is arranged below thelevel 22 of the dense bed 18 and is adjacent the top of the overflowwell 28. Preferably the top of the inlet 64 is arranged at or slightlybelow the bottom of the vertical slots 32 in the upper portion of theoverflow well 23. The main body of the mixing tube 62 slopes downwardlyand its outlet end 66 is arranged above the grid member 16 and adjacentthe outlet end of the solids inlet pipe 26.

In operation, the catalyst from the dense fluidized bed 18 enters theinlet 64 of the mixing tube 62 and gas disengages from the catalystbecause no fluidizing gas is supplied to the mixing tube 62. Due to thedisengagement of the gas the density of the fluidized mixture ofcatalyst in the mixing tube 62 is increased and because of the increasein density there is a driving force available for circulating thecatalyst from the upper portion of the bed 18 near the overflow Well tothe point of discharge 66 near the inlet line 26. In this way highcirculation rates may be provided and improved lateral mixing of thecatalyst in the dense fluidized bed 18 is obtained. The more nearlyregenerated catalyst adjacent the overflow well 32 is returned to thezone or region near the outlet of the inlet line 26 where it isbackmixed with spent or fouled catalyst and better mixing of the spentand regenerated catalyst is provided in this way and the gradient ofcoke on catalyst across vessel 10 is minimized and substantially uniformoxygen content in the flue gas over the entire area of the dense bed 18is obtained.

While only one mixing tube is shown in the drawing more than one suchmixing tube may be used. Also while the mixing tube is shown as spacedinwardly from the overflow 28 in FIG. 1 it may be arranged at eitherside of the overflow well 28 adjacent to the vertical wall of reactionvessel 10. Looking at FIG. 2 the inlet portion 64 of the mixing tube 62may be arranged in front of the overflow well 28 adjacent the wall ofreaction vessel 10 as at 72 or it may be behind the overflow well 28 asat 74 and if two such mixing tubes are used they may be arranged in thismanner with both discharge outlets being adjacent the outlet of theinlet line 26.

In a specific example the reaction vessel 10 has a height from thedistribution grid 16 to the top of the straight vertical side 63 of 30feet and has a diameter of about 20 feet. The inlet line 26 has adiameter of about 2 feet and extends about 3 feet above the distributiongrid 16. The overflow well 28 has a diameter of about 3 feet and fromthe distribution grid 16 to the top of the slots 32 is about 14 feet.The slots 32 are about 1 foot deep.

The mixing tube 62 has a main diameter of about 2 feet with the inlet 64enlarged to about 4 feet. The top of the inlet 64 is arranged about 12feet above distribution grid 16 and about 1 foot below the bottom of thevertical slots 32 in the overflow well 28. The discharge end or outletend 66 of the mixing tube 62 is arranged about 1 to 2 feet from theinlet line 26 and the bottom of the discharge end 66 is about 0.5 footabove the distribution grid 16.

Using conventional synthetic silica alumina gel having an averageparticle size of about 50 to 90 microns and with the superficialvelocity of the air passing up through the dense fluidized bed 18 ofabout 2.5 feet per second and with the temperature in the dense bed 18being about 1125 F. the density of the fluidized bed mixture 18 will beabout 25 lbs. per cubic foot. As the catalyst enters the inlet end 64 ofthe mixing tube 62, deaeration of the catalyst mixture will occur andthe more dense mixture of about 43 lbs. per cubic foot will create apressure or driving force which discharges the catalyst mixture from theoutlet end 62 adjacent the inlet 26 for the fouled or spent catalystfrom the reactor. With a vertical height of the mixing tube 62 from theinlet 64 to outlet 66 equal to about feet, a circulation driving forceof about 1.25 lbs. per square inch will be developed by the catalystparticles in mixing tube 62 and where the dense bed 18 contains about 54tons of catalyst hold up, the rate of circulation through the specificmixing tube described will be about 1200 tons per hour.

The invention is not to be limited to the specific mixing tube given inthe example as larger or smaller mixing tubes may be used and more thanone mixing tube may be used to obtain any desired rate of circulation ofsolids within the dense fluidized bed 18. While the invention has beenspecifically described in connection with the regeneration of spentcatalyst, it is to be understood that the invention may be used withother reactions where better lateral mixing of the catalyst particles isdesired.

While the invention has been described in connection with a specificdesign and arrangement, the invention is not to be restricted therto asin some instances the solid particles from the upper portion of thefluidized bed above the inlet line 26 may be passed through a reverseslanting mixing tube 62 to above the grid member 16 adjacent the bottomportion of overflow well 28. That is, in FIG. 1 the flared or expandedinlet 64 of mixing tube would be at the left near the top of thefluidized bed 18, the mixing tube would slant in the opposite direction,toward the right in FIG. 1 and the discharge end 66 would be on theright in FIG. 1 adjacent the top of grid member 16 and near the bottomof overflow well line 28. Thus in a regeneration zone, for example,partially regenerated spent catalyst particles from the region aboveinlet 26 would be directed down to the bottom portion of the fluid bed18 near the bottom of overflow line 28 and above grid member 16 toobtain better lateral mixing of the catalyst particles in the fluid bed18 and minimize or prevent afterburning.

This case is filed as a continuation-in-part of Borey application SerialNo. 456,207, filed September 15, 1954, which issued on November 24,1959, as U.S. Patent No. 2,914,387.

What is claimed is:

1. A method of contacting finely divided solids and gasiform materialwhich includes maintaining a fluidized dense bed of solids in a reactionzone, introducing solids into the lower portion of said fluidized bed atone side of said reaction zone, withdrawing solids from the upperportion of said fluidized bed of solids at the opposite side of saidreaction zone, collecting solids from the upper portion of saidfluidized bed of solids adjacent the region of withdrawal of solids fromsaid fluidized bed, effecting partial deaeration of said collectedsolids to form a more dense fluidized mixture and flowing such moredense mixture as a confined inclined stream within said dense fluidizedbed to the lower portion of said fluidized dense bed of solids adjacentthe region of introduction of solids to said dense fluidized bed.

2. A method according to claim 1 wherein said inclined stream is at anangle between about 20 and to the horizontal.

3. A method according to claim 1 wherein said reaction Zone comprises aregeneration zone and said finely divided solids comprise crackingcatalyst.

4. In a method of regenerating finely divided catalyst particles from ahydrocarbon conversion operation wherein catalyst particles aremaintained in a dense fluidized condition in a regeneration zone byupflowing oxidizing gas and fouled catalyst particles to be regeneratedare introduced into the lower portion only of said dense fluidized bedand at one side thereof and regenerated catalyst particles are withdrawnfrom the upper portion only of said dense fluidized bed, the improvementfor minimizing afterburning which comprises circulating regeneratedcatalyst particles within said dense fluidized bed from near the regionof withdrawal of regenerated catalyst particles to near the region ofintroduction of fouled catalyst particles as a confined stream withinsaid dense fluidized bed and inclined to the horizontal between about 20and 70 to obtain improved mixing of the fouled and regenerated catalystparticles.

5. In a method of contacting finely divided solids and gasiform materialwhich includes maintaining a dense fluidized bed of solids in a reactionzone by upflowing gasiform material and solids are introduced into oneportion of said dense fluidized bed and solids are withdrawn fromanother portion of said dense fluidized bed, the improvement forobtaining better lateral mixing of the solids in said dense fluidizedbed which comprises circulating solids within said fluidized bed byflowing a confined inclined stream of solids of higher density than thator" said dense fluidized bed and within said dense fluidized bed fromnear the upper portion of said dense fluidized bed at one side of saiddense fluidized bed to near the lower portion of said dense fluidizedbed at the opposite side of said dense fluidized bed.

6. A method of contacting finely divided solids and gasiform materialwhich includes maintaining a fluidized dense bed of solids in acontacting zone, introducing solids to be treated into the lower portiononly of said fluidized bed, withdrawing solids from an upper portiononly of said fluidized bed of solids, collecting solids from an upperportion of said fluidized bed of solids, eflecting partial deaeration ofsaid collected solids to form a more dense fluidized mixture and flowingsuch more dense mixture as a confined downwardly flowing stream withinsaid dense fluidized bed to the lower portion of said fluidized densebed of solids within said contacting zone near the region ofintroduction of solids thereto.

References Cited in the file of this patent UNITED STATES PATENTS2,689,823 Hardy et a1 Sept. 21, 1954

4. IN A METHOD OF REGENERATING FINELY DIVIDED CATALYST PARTICLES FROM AHYDROCARBON CONVERSION OPERATION WHEREIN CATALYST PARTICLES AREMAINTAINED IN A DENSE FLUIDIZED CONDITION IN A REGENERATION ZONE BYUPFLOWING OXIDIZING GAS AND FOULED CATALYST PARTICLES TO BE REGENERATEDARE INTRODUCED INTO THE LOWER PORTION ONLY OF SAID DENSE FLUIDIZED BEDAND AT ONE SIDE THEREOF AND REGENERATED CATALYST PARTICLES ARE WITHDRAWNFROM THE UPPER PORTION ONLY OF SAID DENSE FLUIDIZED BED, THE IMPROVEMENTFOR MINIMIZING AFTERBRUNING WHICH COMPRISES CIRCULATING REGENERATEDCATALYST PARTICLES WITHIN SAID DENSE FLUIDIZED BED FROM NEAR THE REGIONOF WITHDRAWAL OF REGENERATED CATALYST PARTICLES TO NEAR THE REGION OFINTRODUCTION OF FOULED CATALYST PARTICLES AS A CONFINED STREAM WITHINSAID DENSE FLUIDIZED BED AND INCLINED TO THE HORIZONTAL BETWEEN ABOUT20* AND 70* TO OBTAIN IMPROVED MIXING TO THE FOULED AND REGENERATEDCATALYST PARTICLES.